12.4.3 Human Gas Exchange: The Roles of Respiratory Pigments Flashcards
1
Q
Human Gas Exchange: The Roles of Respiratory Pigments
A
- The respiratory pigment hemoglobin is ideal as an oxygen carrier for the respiratory system because it can bind with and transport oxygen and then release it when needed.
- During exercise, the pH of blood decreases. This decrease causes hemoglobin to give up oxygen more readily so that it may be delivered to tissues in oxygen need. The effect of pH on hemoglobin is referred to as the Bohr shift.
- Myoglobin is an oxygen-carrying protein found in muscles. It has a greater affinity for oxygen than hemoglobin; thus, it will give up most of its oxygen only when concentrations get very low in the muscles.
2
Q
respiratory pigments
A
- Respiratory pigments are proteins that carry oxygen in the blood. The color of these pigments is due to metal ions found within them.
- Shown on the left is hemoglobin, a respiratory pigment found in nearly all vertebrates. Hemoglobin is made up of four polypeptide subunits. Within each subunit is a heme group, which is a cofactor containing an iron atom in its center. The iron atom is able to bind to oxygen that diffuses across the alveoli membranes in the lungs.
3
Q
partial pressure
A
- The chart to the left shows the percent oxygen concentration of hemoglobin in tissues with varying partial pressures of oxygen. Partial pressure is a value that corresponds to the concentration of a gas measured in mm Hg.
- Notice that hemoglobin is fully saturated in the lungs where the partial pressure of oxygen is at its highest (100 mm Hg). At the partial pressure of tissues at rest (40 mm Hg), hemoglobin is still highly saturated. Tissues at rest don’t require as much oxygen as active tissues; thus, hemoglobin gives up only a small percentage of its oxygen.
- Tissues during exercise require more oxygen, thereby leading to a lower partial pressure (<20 mm Hg). In tissues with very low partial pressures, hemoglobin quickly gives up more oxygen, resulting in a lower percent oxygen concentration
4
Q
bohr shift
A
- During exercise the pH of the blood decreases because carbon dioxide produced from respiration combines with water to form carbonic acid. The increase in hydrogen ions in the blood causes the hemoglobin to give up more oxygen at any given partial pressure in order to support the high level of respiration taking place in tissues during exercise. This shift in oxygen release by hemoglobin in response to a decrease in pH is referred to as the Bohr shift and is shown on the graph as the shift from the dashed line to the solid line.
5
Q
myoglobin
A
- Myoglobin is an oxygen-storing protein found in muscles. As shown in the graph, myoglobin has a higher affinity for oxygen at a given partial pressure than hemoglobin. Notice that myoglobin releases most of its oxygen in muscles that have very low partial pressures. These tissues have a very high need for oxygen.
6
Q
In which organ or structure is hemoglobin most completely saturated with oxygen?
A
- lung
7
Q
Which of the following is not a characteristic of hemoglobin?
A
- It has an irreversible affinity for oxygen
8
Q
Heme is
A
- a non-polypeptide cofactor
9
Q
In the lungs, hemoglobin reaches what oxygen saturation level?
A
- 100%
10
Q
Since oxygen, like other solutes, can dissolve directly into blood, what is the advantage of having hemoglobin act as an oxygen carrier?
A
- Hemoglobin keeps the oxygen levels in the blood higher than it would be if oxygen dissolved in the blood directly
11
Q
Which of the following has the highest affinity for oxygen?
A
- tissues during exercise
12
Q
PO2 represents the partial pressure of oxygen. Another way to think of PO2 is as:
A
- the concentration of oxygen.
13
Q
During exercise, which of the following occur to reduce hemoglobin’s affinity for oxygen?
A
- Carbon dioxide (CO2 ) concentrations increase.
- pH decreases.
- H + reacts with saturated hemoglobin.
